PGMA-grafted MWCNTs: correlation between molecular weight of grafted PGMA and dispersion state of MWCNTs–PGMA in an epoxy matrix

The correlationship between molecular weight of surface-grafted polyglycidyl methacrylate (PGMA) and dispersion state of PGMA-grafted MWCNTs (MWCNTs–PGMA) was systematically investigated and revealed in this work. Initially, the MWCNTs–PGMA with different PGMA molecular weights were successfully prepared via surface-initiated atom transfer radical polymerization (ATRP) by changing reaction times. Then, a feasible and efficient approach to quantitatively measure the molecular weight of surface-grafted PGMA onto insoluble MWCNTs was proposed by properly analyzing X -ray photoelectron spectroscope (XPS) and thermos-gravimetric analyzer (TGA) data. The molecular weight of the surface-grafted PGMA ranged from 3123 to 13,840 g/mol based on TGA data and varied from 3814 to 9979 g/mol based on XPS data. Subsequently, the characterization results of optical microscope (OM), UV–Vis spectroscopy and dynamic light scattering (DLS) indicated that the pre-dispersion state of MWCNTs–PGMA in PMMA solution was clearly enhanced with the molecular weight of grafted PGMA increasing due to the physical transition from “dry-brush” miscibility to “wet brush” miscibility between PGMA and PMMA. Therefore, benefiting from the outstanding compatibility and interactions between surface-grafted PGMA and EP matrix, the highest enhancement in mechanical properties of EP composites was achieved when using MWCNTs–PGMA-3 with largest PGMA molecular weight as the reinforcement. The failure behavior of EP composites was comprehensively resulted from the efficient stress transfer and microcrack propagation by MWCNTs–PGMA as well as the additional chemical bonding offered by surface-grafted PGMA. Graphical abstract